Production method of thin-walled low-smoke zero-halogen dry loose tube

Abstract

The present invention relates to a production method of a thin-walled low-smoke and halogen-free dry loose tube. This technical solution optimizes the die drawing ratio, reduces the head pressure, and makes the discharging uniform and balanced. When producing a large number of cores, through the methods of optical fiber segmentation and decreasing tension, the loose tube does not bend or twist, avoiding the situations of snake shape, S shape, and inconsistent extra length. The loose tube produced by this technical solution has good molding, smooth appearance, uniform wall thickness, thin tube wall, and small shrinkage of the tube sheath. Moreover, it is a dry structure without grease filling, the tube wall thickness is very thin, with a minimum of 0.13 mm. This technical solution has a large optical fiber capacity, low cost, and is convenient for large-scale popularization and application.

Description

Technical Field

[0001] This invention relates to a method for producing loose-sleeve pipes, specifically a method for producing thin-walled, low-smoke, halogen-free dry loose-sleeve pipes. Background Technology

[0002] Loose tubes are sleeves made of polypropylene or nylon used in optical cables to loosely house optical fibers and protect them from internal stress and external lateral pressure. They are typically only visible after the cable sheath has been removed and are primarily used to protect the optical fibers. With the rapid development of the communications industry, the requirements for optical cables are becoming increasingly stringent, especially regarding reducing cable diameter. This places higher demands on cable production, particularly on reducing the thickness of loose tubes. Currently, dry-type loose tubes (non-grease-filled) typically have a relatively large wall thickness, usually around 0.3mm. The advantages of this are twofold: firstly, it is easier to manufacture; if the wall thickness is too thin, the tube is prone to breakage, resulting in more defective products. Secondly, a thicker wall ensures stable shrinkage, preventing the tube from twisting at room temperature. However, current technology... The following technical problems exist in the production of thin-walled loose tubes: 1) Due to the thin wall of the loose tube, it is easy for the tube to twist into an S-shape during production; 2) The excess length is inconsistent and difficult to control; 3) The produced loose tubes have a segmented appearance and uneven thickness; 4) The produced loose tubes have uneven wall thickness and are prone to tearing; 5) The debugging process during production is long and wasteful of materials. In view of the rapid development of the current communication industry and the increasing demand for communication capacity, it is particularly important to develop a thin-walled, low-smoke, halogen-free loose tube that can accommodate more optical fibers and provide communication capacity under the same size. Summary of the Invention

[0003] This invention addresses the problems existing in the prior art by providing a production method for thin-walled, low-smoke, halogen-free dry loose tubes. This process is ingeniously designed, easy to operate, improves the pass rate of loose tubes, reduces material waste and loss, produces well-formed tubes, eliminates S-shaped defects after fiber threading, and results in a smooth appearance.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for producing thin-walled, low-smoke, halogen-free dry loose-sleeve pipes, characterized in that the method includes the following steps:

[0005] 1) Adjust the pay-off frame, that is, adjust the 1-16 fiber pay-off frames. Place the 1-16 spools of colored fiber on the shaft of each pay-off frame, fix them, and adjust the position of the fiber so that the 1-16 fibers can be aligned with the center of the fiber optic bundle. Set the pay-off tension value of the 1-16 fibers to 0.5N on the touch screen of the pay-off tension control device.

[0006] 2) Adjust the extruder, pour the low-smoke halogen-free material into the hopper, and set the extruder temperature. The extruder consists of a body and a head. The body has 3 heating sections, and the head has 2 heating sections, for a total of 5 heating sections. The heating temperatures are set to 140℃, 160℃, 165℃, 170℃, and 178℃ respectively. Prepare the fiber optic hub, fiber optic preheating device, hot and cold water tank, wheel traction, take-up tensioning device, and double-reel take-up machine. The fiber optic hub is set between the fiber optic pay-off frame and the fiber optic preheating device. The hot and cold water tank, wheel traction, take-up tensioning device, and double-reel take-up machine are sequentially set behind the extruder.

[0007] 3) Turn on the extruder switch. The extruder starts working and the material is extruded from the die head to form a hollow tube. While the extruder is working, the employee pulls the hollow tube forward by hand at a constant speed (20m / min). After passing through the hot and cold water tank, it enters the wheel traction system. In this way, there is a hollow tube among the three devices: extruder, hot and cold water tank, and wheel traction system, which is in preparation for inserting optical fiber later.

[0008] 4) Fiber insertion: This step uses segmented fiber insertion with decreasing tension. The specific operation is as follows: Set the number of cores in the loose tube to N (N is an integer from 2 to 16). First, set the fiber tension to 0.5N. After inserting N fibers through the fiber optic hub, fix them in place. The fiber preheating device is used to dry the fibers to prevent moisture from adhering to the fiber surface and affecting transmission performance. During production, the fibers pass through the preheating device and then enter the extruder head. During production, first insert two fibers, passing through the preheating device and the extruder head, until they reach the fiber in step 3) which is ready. After inserting 9-11 meters of fiber into the empty sleeve, ensure that the fiber will not be detached from the sleeve due to the tension of the fiber release. After confirming that the fiber has reached the position of the wheel traction, the sleeve will generate a certain tension due to the presence of the fiber. Adjust the extrusion amount of the extruder to match the production speed, and prepare to insert the remaining (N-2) fibers. Using the same method as the previous 2 fibers, insert the remaining fibers into the sleeve, and quickly change the fiber release tension from 0.5N to 0.15N on the touch screen. Check the appearance of the sleeve.

[0009] 5) Check the outer diameter display value on the diameter measuring instrument at the wheel traction position. After adjusting the extrusion amount to adjust the outer diameter to the required value, the sleeve with N core optical fibers is passed through the take-up tensioning device and then enters the take-up reel of the double-reel take-up machine. Start the take-up machine and the take-up tensioning device controls the take-up speed of the take-up machine to take up the wire. At this point, the loose sleeve production process is completed.

[0010] 6) Conduct excess length testing on the product.

[0011] This technical solution proposes a manufacturing method for a thin-walled, low-smoke, halogen-free dry loose tube, which controls the tube wall thickness between 0.13 and 0.18 mm. The tube can accommodate up to 16 ordinary optical fibers without affecting their performance, making it convenient to use.

[0012] In existing technology, a 12-core wire feeding frame is typically used, with the rotation of each wire feeding frame controlled by a Danfoss frequency converter. After the upgrade, a set of 4-core wire feeding frames is added to the original 12-core frame, placed side by side and interconnected with the original wire feeding frame. The speed control is changed to be controlled by a Panasonic servo, which can better stabilize the wire feeding. The servo is connected to a touch screen, which allows for precise control of the tension and its value.

[0013] This technical solution employs a segmented fiber optic cable and a decreasing tension method. The empty tube formed in step 3) has poor tensile strength. If 16 fibers are inserted at once, the tensile force of these fibers will be very high, reaching 8N, easily breaking the empty tube after insertion. The high tensile force of 16 fibers cannot guarantee that the fibers will not spring back and be pulled out of the tube before entering the wheel-type traction system. If a very small tension value is set initially, such as 0.15N, the vibration during fiber laying will be severe, causing the control mechanism on each laying reel on the laying frame to vibrate significantly, potentially breaking or causing the fibers to jump out of the control mechanism. Only after the fiber laying is stable can the tension value be reduced to minimize vibration and prevent fiber breakage. Inserting two fibers first ensures the empty tube in step 3) has sufficient tension to prevent breakage by subsequent fiber insertions, facilitating proper forming. This method allows for relatively stable laying and tube production, ensuring a smooth appearance without S-shaped defects or other undesirable phenomena.

[0014] As an improvement to this invention, the hot and cold water tank in step 3) is operated as follows: the total length of the hot and cold water tank is 16 meters, including a 4-meter hot water tank and a 12-meter cold water tank. The tanks are filled with water, and the casing is submerged in the water, which serves to cool and crystallize the casing. The hot water tank is located closer to the extruder head, and its heating temperature is set at 60-65℃. This is because the optimal crystallization temperature for low-smoke halogen-free materials is 60℃-70℃, at which temperature they can crystallize well, reducing the shrinkage of the casing. The cold water tank is at room temperature, 18-22℃. This creates a temperature difference between the hot and cold water tanks, facilitating secondary crystallization of the low-smoke halogen-free material and making shrinkage more stable.

[0015] As an improvement of the present invention, the extruder head is provided with a die with a draw ratio of 2-3. The die includes an outer die and an inner die, wherein the outer die has a size of D1, the inner die has a size of D2, the outer diameter of the sleeve is d1, and the inner diameter of the sleeve is d2, i.e., DDR (draw ratio) = This draw ratio is beneficial for the forming of loose tubes, and the pressure is low, making it easy to form thin-walled sheaths. By changing the angle between the inner and outer dies to a near-parallel angle, the pressure of low-smoke halogen-free materials during extrusion can be reduced, allowing for smooth material extrusion. By designing reasonable inner and outer die dimensions, the draw ratio can be between 2 and 3, which is beneficial for the forming of loose tubes.

[0016] As an improvement of the present invention, the specific operation of the excess length test in step 6 is as follows: the excess length test refers to the difference between the length of the optical fiber and the length of the sleeve: take a section of sleeve containing optical fiber, the length of which is recorded as L1, pull out the optical fiber, the length of which is recorded as L2, L2-L1=Δ, Δ is the excess length of the optical fiber, Δ / L1≤1‰, that is, the product is qualified.

[0017] This technical solution incorporates excess length testing to reduce its impact on fiber optic attenuation. Because the sheath material is low-smoke halogen-free, and undergoes high-temperature extrusion followed by water cooling, the material's inherent properties dictate a certain degree of shrinkage. Since optical fiber is a silicon dioxide crystal, it does not shrink. This results in the optical fiber being longer than the sheath, causing some bending within the sheath. Therefore, the excess fiber length cannot be too large, as this will affect fiber attenuation. A suitable excess length value is 1‰, i.e., Δ / L1 ≤ 1‰.

[0018] The factors affecting the excess length are as follows: material properties and the amount of material retraction; high fiber tension results in a small excess length, while low tension results in a large excess length; the extruder die head and the pressure during material extrusion also affect the sleeve retraction—low pressure results in a small excess length, and high pressure results in a large excess length. Therefore, the design of a die with a draw ratio of 2-3 is to reduce the pressure inside the die. This technical solution, through clever design, minimizes the excess length value and further ensures product quality.

[0019] Compared with existing technologies, the advantages of this invention are as follows: 1) The entire technical solution is ingeniously designed and easy to operate; 2) This technical solution can reduce losses during production debugging, and once debugged, it can achieve stable production for a long time; 3) This technical solution optimizes the mold stretching ratio, reduces the pressure of the die head, and makes the output uniform and balanced; 4) When producing large core counts, the fiber segmentation and tension reduction methods prevent the sleeve from bending or twisting, avoiding the formation of serpentine or S-shaped shapes and inconsistent excess lengths; 5) The loose tubes produced by this technical solution have good forming, smooth appearance, uniform wall thickness, thin tube walls, and shrinkage of the sleeve sheath; 6) This technical solution is a dry structure, without grease filling, and the sleeve wall thickness is very thin, with a minimum of 0.13mm; 7) This technical solution has a large fiber capacity, low cost, and is easy to promote and apply on a large scale. Attached Figure Description

[0020] Figure 1This is a flowchart of the entire process of this invention;

[0021] Figure 2 This is a schematic diagram of the loose sleeve structure;

[0022] Figure 3 This is a schematic diagram of the outer and inner mold structures;

[0023] In the diagram: 1. Fiber optic cable laying frame, 2. Fiber optic cable preheating device, 3. Extruder, 4. Hot and cold water tank, 5. Wheel traction, 6. Take-up tensioning device, 7. Double-reel take-up machine, 8. Outer sheath, 9. Colored fiber optic cable. Detailed Implementation

[0024] To enhance understanding of the invention, the invention will be further described and introduced below with reference to the accompanying drawings.

[0025] Example 1: A method for producing a thin-walled, low-smoke, halogen-free dry loose-sleeve pipe, the method comprising the following steps:

[0026] 1) Adjust the pay-off frame, that is, adjust the 1-16 fiber pay-off frame 1, place the 1-16 spools of colored fiber 9 on the shaft of each pay-off frame, fix them, and adjust the position of the fiber optics so that the 1-16 fiber optics can be aligned with the center of the fiber optic bundle; set the pay-off tension value of the 1-16 fiber optics to 0.5N on the touch screen of the pay-off tension control device.

[0027] 2) Adjust the extruder 3, pour the low-smoke halogen-free material into the hopper, and set the extruder temperature. The extruder 3 consists of a machine body and a die head. The machine body is divided into 3 heating sections, and the die head is divided into 2 heating sections, for a total of 5 heating sections. The heating temperatures are set to 140℃, 160℃, 165℃, 170℃, and 178℃ respectively. Prepare the fiber optic hub, fiber optic preheating device, hot and cold water tank, wheel traction, take-up tensioning device, and double-reel take-up machine. The fiber optic hub is set between the fiber optic pay-off frame and the fiber optic preheating device. The hot and cold water tank, wheel traction, take-up tensioning device, and double-reel take-up machine are arranged sequentially behind the extruder.

[0028] 3) Turn on the extruder switch. The extruder starts working and the material is extruded from the die head to form a hollow tube. While the extruder is working, the employee pulls the hollow tube forward by hand at a constant speed (20m / min). After passing through the hot and cold water tank, it enters the wheel traction system. In this way, there is a hollow tube among the three devices: extruder, hot and cold water tank, and wheel traction system, which is in preparation for inserting optical fiber later.

[0029] 4) Fiber insertion: This step uses segmented fiber insertion with decreasing tension. The specific operation is as follows: Set the number of cores in the loose tube to N (N is an integer from 2 to 16). First, set the fiber tension to 0.5N. After inserting N fibers through the fiber optic hub, fix them in place. The fiber preheating device is used to dry the fibers to prevent moisture from adhering to the fiber surface and affecting transmission performance. During production, the fibers pass through the preheating device and then enter the extruder head. During production, first insert two fibers, passing through the preheating device and the extruder head, into the section prepared in step 3). After inserting 9-11 meters of fiber into a good empty sleeve, ensure that the fiber will not be detached from the sleeve due to the tension of the fiber release. After confirming that the fiber has reached the position of the wheel traction, the sleeve will generate a certain tension due to the presence of the fiber. Adjust the extrusion amount of the extruder to match the production speed, and prepare to insert the remaining N-2 fibers. Using the same method as the previous 2 fibers, insert the remaining fibers into the sleeve, and quickly change the fiber release tension from 0.5N to 0.15N on the touch screen. Check the appearance of the sleeve.

[0030] In this embodiment, when N is 16, taking the production of a 16-core loose tube as an example, first confirm that the fiber tension is 0.5N, then pass the 16 optical fibers through the fiber optic hub and fix them in place. The hub is located at... Figure 1 Between the fiber optic preheating device 2 and the fiber optic pay-off frame 1, the fiber optic preheating device 2 is used to dry the fiber optic cable, preventing moisture from adhering to the fiber optic surface and affecting its transmission performance. During production, the fiber optic cable passes through the preheating device 2 and then enters the extruder head. Two fibers are first threaded through the preheating device 2 and the extruder head 3 into a pre-prepared empty sleeve. After approximately 10 meters, it is ensured that the fiber optic cable will not detach from the sleeve due to the pay-off tension. After confirming that the fiber optic cable has reached the position of the wheel traction 5, the sleeve will then experience a certain tension due to the presence of the fiber optic cable. The extrusion rate of the extruder is adjusted to match the production speed. The remaining 14 fibers are then threaded into the sleeve using the same method as the previous two fibers. The pay-off tension of the fiber optic cable is quickly changed from 0.5N to 0.15N on the touch screen, and the appearance of the sleeve is checked.

[0031] 5) Check the outer diameter display value on the diameter measuring instrument at the wheel traction position. After adjusting the extrusion amount to adjust the outer diameter to the required value, the sleeve with 16 core optical fibers is passed through the take-up tensioning device and then enters the take-up reel of the double-reel take-up machine. Start the take-up machine and the take-up tensioning device controls the take-up speed to take up the wire. At this point, the loose sleeve production process is complete.

[0032] 6) Conduct excess length testing on the product.

[0033] This technical solution proposes a manufacturing method for a thin-walled, low-smoke, halogen-free dry loose tube, which controls the tube wall thickness between 0.13 and 0.18 mm. The tube can accommodate up to 16 ordinary optical fibers without affecting their performance, making it convenient to use.

[0034] In existing technology, a 12-core wire feeding frame is typically used, with the rotation of each wire feeding frame controlled by a Danfoss frequency converter. After the upgrade, a set of 4-core wire feeding frames is added to the original 12-core frame, placed side by side and interconnected with the original wire feeding frame. The speed control is changed to be controlled by a Panasonic servo, which can better stabilize the wire feeding. The servo is connected to a touch screen, which allows for precise control of the tension and its value. This technical solution employs a segmented fiber optic cable and a decreasing tension method. The empty tube formed in step 3) has poor tensile strength. If 16 fibers are inserted at once, the tensile force of these fibers will be very high, reaching 8N, easily breaking the empty tube after insertion. The high tensile force of 16 fibers cannot guarantee that the fibers will not spring back and be pulled out of the tube before entering the wheel-type traction system. If a very small tension value is set initially, such as 0.15N, the vibration during fiber laying will be severe, causing the control mechanism on each laying reel on the laying frame to vibrate significantly, potentially breaking or causing the fibers to jump out of the control mechanism. Only after the fiber laying is stable can the tension value be reduced to minimize vibration and prevent fiber breakage. Inserting two fibers first ensures the empty tube in step 3) has sufficient tension to prevent breakage by subsequent fiber insertions, facilitating proper forming. This method allows for relatively stable laying and tube production, ensuring a smooth appearance without S-shaped defects or other undesirable phenomena.

[0035] Example 2: As an improvement of the present invention, the hot and cold water tank in step 3) is operated as follows: The total length of the hot and cold water tank is 16 meters, of which the hot water tank is 4 meters and the cold water tank is 12 meters. The tank is filled with water, and the casing is immersed in the water, which serves to cool and crystallize the casing. The hot water tank is closer to the extruder head. The heating temperature of the hot water tank is set to 60-65℃, because the optimal crystallization temperature of low-smoke halogen-free materials is 60℃-70℃. At this temperature, low-smoke halogen-free materials can crystallize well, reducing the shrinkage of the casing. The cold water tank temperature is room temperature, 18-22℃. In this way, there is a temperature difference between the hot water tank and the cold water tank when the casing passes through the hot water tank, which facilitates the secondary crystallization of low-smoke halogen-free materials and makes the shrinkage more stable.

[0036] Example 3: As an improvement of the present invention, the extruder head is provided with a die with a draw ratio of 2-3. The die includes an outer die and an inner die, wherein the outer die has a size of D1, the inner die has a size of D2, the outer diameter of the sleeve is d1, and the inner diameter of the sleeve is d2, i.e., DDR (draw ratio) = Taking a 16-core thin-walled low-smoke halogen-free loose-sleeve tube as an example, the die dimensions are D1=2.1mm, D2=1.6mm, and the required outer diameter of the loose-sleeve tube is d1=1.55mm, d2=1.25mm. Substituting into the above formula, DDR=2.2, that is, the draw ratio is 2.2. Such a loose-sleeve tube can achieve a thinner wall thickness and a round appearance. This draw ratio is beneficial to the forming of the loose-sleeve tube, and the pressure is low, making it easy to form a thin-walled sheath. By changing the included angle between the inner and outer dies to a near-parallel angle, the pressure when the low-smoke halogen-free material is extruded from the die can be reduced, allowing the material to be extruded smoothly. Designing reasonable inner and outer die dimensions so that the draw ratio is between 2 and 3, such a small draw ratio is beneficial to the forming of the loose-sleeve tube.

[0037] Example 4: As an improvement of the present invention, the specific operation of the excess length test in step 6 is as follows. The excess length test refers to the difference between the length of the optical fiber and the length of the sleeve: Take a section of sleeve containing optical fiber, and record the length as L1. Pull out the optical fiber and record the length of the optical fiber as L2. L2-L1=Δ, and Δ is the excess length of the optical fiber. If Δ / L1≤1‰, the product is qualified.

[0038] This technical solution incorporates excess length testing to reduce its impact on fiber optic attenuation. Because the sheath material is low-smoke halogen-free, and undergoes high-temperature extrusion followed by water cooling, the material's inherent properties dictate a certain degree of shrinkage. Since optical fiber is a silicon dioxide crystal, it does not shrink. This results in the optical fiber being longer than the sheath, causing some bending within the sheath. Therefore, the excess fiber length cannot be too large, as this will affect fiber attenuation. A suitable excess length value is 1‰, i.e., Δ / L1 ≤ 1‰.

[0039] The factors affecting the excess length are as follows: material properties and the amount of material retraction; high fiber tension results in a small excess length, while low tension results in a large excess length; the extruder die head and the pressure during material extrusion also affect the sleeve retraction—low pressure results in a small excess length, and high pressure results in a large excess length. Therefore, the design of a die with a draw ratio of 2-3 is to reduce the pressure inside the die. This technical solution, through clever design, minimizes the excess length value and further ensures product quality.

[0040] The present invention can also combine at least one of the technical features described in Embodiments 2, 3, and 4 with Embodiment 1 to form new implementation methods.

[0041] It should be noted that the above embodiments are not intended to limit the scope of protection of the present invention. Equivalent transformations or substitutions made based on the above technical solutions all fall within the scope of protection of the claims of the present invention.

Claims

1. A method for producing thin-walled, low-smoke, halogen-free dry loose-sleeve pipes, characterized in that, The method includes the following steps: 1) Adjust the pay-off frame, that is, adjust the 1-16 fiber pay-off frames. Place the 1-16 spools of colored fiber on the shaft of each pay-off frame, fix them, and adjust the position of the fiber so that the 1-16 fibers can be aligned with the center of the fiber optic bundle. Set the pay-off tension value of the 1-16 fibers to 0.5N on the touch screen of the pay-off tension control device. 2) Adjust the extruder, pour the low-smoke halogen-free material into the hopper, and set the extruder temperature. The extruder consists of a body and a head. The body has 3 heating sections, and the head has 2 heating sections, for a total of 5 heating sections. The heating temperatures are set to 140℃, 160℃, 165℃, 170℃, and 178℃ respectively. Prepare the fiber optic hub, fiber optic preheating device, hot and cold water tank, wheel traction, take-up tensioning device, and double-reel take-up machine. The fiber optic hub is set between the fiber optic pay-off frame and the fiber optic preheating device. The hot and cold water tank, wheel traction, take-up tensioning device, and double-reel take-up machine are sequentially set behind the extruder. 3) Turn on the extruder switch. The extruder starts working and the material is extruded from the die head to form a hollow tube. While the extruder is working, the employee pulls the hollow tube forward by hand at a constant speed of 20m / min. After passing through the hot and cold water tank, it enters the wheel traction system. In this way, there is a hollow tube among the three devices: extruder, hot and cold water tank, and wheel traction system, which is in preparation for inserting optical fiber later. 4) Fiber insertion: This step uses segmented fiber insertion with decreasing tension. The specific operation is as follows: Set the number of cores in the loose tube to N (N is an integer from 2 to 16). First, set the fiber tension to 0.5N. After inserting N fibers through the fiber optic hub, fix them in place. The fiber preheating device is used to dry the fibers to prevent moisture from adhering to the fiber surface and affecting transmission performance. During production, the fibers pass through the preheating device and then enter the extruder head. During production, first insert two fibers, passing through the preheating device and the extruder head, until they reach the fiber in step 3) which is ready. After inserting 9-11 meters of fiber into the empty sleeve, ensure that the fiber will not be detached from the sleeve due to the tension of the fiber release. After confirming that the fiber has reached the position of the wheel traction, the sleeve will generate a certain tension due to the presence of the fiber. Adjust the extrusion amount of the extruder to match the production speed, and prepare to insert the remaining (N-2) fibers. Use the same method as the previous 2 fibers to insert the remaining fibers into the sleeve. Then, change the fiber release tension from 0.5N to 0.15N on the touch screen and check the appearance of the sleeve. 5) Check the outer diameter display value on the diameter measuring instrument at the wheel traction position. After adjusting the extrusion amount to adjust the outer diameter to the required value, the sleeve with N core optical fibers is passed through the take-up tensioning device and then enters the take-up reel of the double-reel take-up machine. Start the take-up machine and the take-up tensioning device controls the take-up speed of the take-up machine to take up the wire. At this point, the loose sleeve production process is completed. 6) Conduct excess length testing on the product.

2. The production method of the thin-walled, low-smoke, halogen-free dry loose-sleeve pipe according to claim 1, characterized in that, The specific operation of the hot and cold water tank in step 3) is as follows: The total length of the hot and cold water tank is 16 meters, of which the hot water tank is 4 meters and the cold water tank is 12 meters. The tank is filled with water and the sleeve is immersed in the water, which plays a role in cooling and crystallizing the sleeve. The hot water tank is closer to the extruder head. The heating temperature of the hot water tank is set to 60-65℃, and the water temperature of the cold water tank is room temperature, 18-22℃.

3. The method for producing thin-walled, low-smoke, halogen-free dry loose-sleeve pipes according to claim 2, characterized in that, The extruder head is equipped with a die with a draw ratio of 2-3. The die includes an outer die and an inner die, wherein the outer die has a dimension of D1, the inner die has a dimension of D2, the outer diameter of the sleeve is d1, and the inner diameter of the sleeve is d2, i.e., DDR (draw ratio) = .

4. The method for producing thin-walled, low-smoke, halogen-free dry loose-sleeve pipes according to claim 2, 3, or 4, characterized in that, The specific operation of the excess length test in step 6 is as follows: the excess length test refers to the difference between the length of the optical fiber and the length of the sleeve: take a section of sleeve containing optical fiber, and record the length as L1. Pull out the optical fiber and record the length of the optical fiber as L2. L2-L1=Δ, and Δ is the excess length of the optical fiber. If Δ / L1≤1‰, the product is qualified.

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